lnterleukin-1 alpha (IL-1α), interleukin-1 beta (IL-1β), and interleukin-1 receptor antagonist (IL-1ra) each binds to the type 1 IL-1 receptor (IL-1RI), which is found on the surface of certain cell types. IL-1α and IL-1β have physiological effects on a number of different target cells, including certain cells that are involved in the inflammatory and immune responses. IL-1ra, in contrast, binds to IL-1RI, but does not elicit comparable downstream biological responses. Rather, IL-1ra competitively inhibits IL-1α and IL-1β binding to IL-1RI. Anakinra, an E. coli-produced version of IL-1ra, is marketed for treatment of rheumatoid arthritis.